0
Technical Brief

Comparisons of Anterior Plate Screw Pullout Strength Between Polyurethane Foams and Thoracolumbar Cadaveric Vertebrae

[+] Author and Article Information
Srinidhi Nagaraja

Office of Science and Engineering Laboratories,
Division of Applied Mechanics,
Center for Devices and Radiological Health,
U.S. Food and Drug Administration,
10903 New Hampshire Avenue,
Building 62, Room 2210,
Silver Spring, MD 20993-0002

Vivek Palepu

Office of Science and Engineering Laboratories,
Division of Applied Mechanics,
Center for Devices and Radiological Health,
U.S. Food and Drug Administration,
Silver Spring, MD 20993

1Corresponding author.

Manuscript received May 24, 2016; final manuscript received August 5, 2016; published online August 24, 2016. Assoc. Editor: Brian D. Stemper.

J Biomech Eng 138(10), 104505 (Aug 24, 2016) (6 pages) Paper No: BIO-16-1219; doi: 10.1115/1.4034427 History: Received May 24, 2016; Revised August 05, 2016

Synthetic polyurethane foams are frequently used in biomechanical testing of spinal medical devices. However, it is unclear what types of foam are most representative of human vertebral trabecular bone behavior, particularly for testing the bone–implant interface. Therefore, a study was conducted to compare polyurethane foam microstructure and screw pullout properties to human vertebrae. Cadaveric thoracolumbar vertebrae underwent microcomputed tomography to assess trabecular bone microstructure. Spine plate screws were implanted into the vertebral body and pullout testing was performed. The same procedure was followed for eight different densities (grades 5–30) of commercially available closed cell (CCF) and open cell foams (OCF). The results indicated that foam microstructural parameters such as volume fraction, strut thickness, strut spacing, and material density rarely matched that of trabecular bone. However, certain foams provided mechanical properties that were comparable to the cadavers tested. Pullout force and work to pullout for screws implanted into CCF grade 5 were similar to osteoporotic female cadavers. In addition, screw pullout forces and work to pullout in CCF grade 8, grade 10, and OCF grade 30 were similar to osteopenic male cadavers. All other OCF and CCF foams possessed pullout properties that were either significantly lower or higher than the cadavers tested. This study elucidated the types and densities of polyurethane foams that can represent screw pullout strength in human vertebral bone. Synthetic bone surrogates used for biomechanical testing should be selected based on bone quantity and quality of patients who may undergo device implantation.

FIGURES IN THIS ARTICLE
<>
Copyright © 2016 by ASME
Your Session has timed out. Please sign back in to continue.

References

Szivek, J. , Thomas, M. , and Benjamin, J. , 1993, “ Technical Note. Characterization of a Synthetic Foam as a Model for Human Cancellous Bone,” J. Appl. Biomater., 4(3), pp. 269–272. [CrossRef] [PubMed]
Szivek, J. A. , Thompson, J. D. , and Benjamin, J. B. , 1995, “ Characterization of Three Formulations of a Synthetic Foam as Models for a Range of Human Cancellous Bone Types,” J. Appl. Biomater., 6(2), pp. 125–128. [CrossRef] [PubMed]
Hein, T. , Hotchkiss, R. , Perissinotto, A. , and Chao, E. , 1986, “ Analysis of Bone Model Material for External Fracture Fixation Experiments,” Biomed. Sci. Instrum., 23, pp. 43–48.
Johnson, A. E. , and Keller, T. S. , 2008, “ Mechanical Properties of Open-Cell Foam Synthetic Thoracic Vertebrae,” J. Mater. Sci. Mater. Med., 19(3), pp. 1317–1323. [CrossRef] [PubMed]
Calvert, K. L. , Trumble, K. P. , Webster, T. J. , and Kirkpatrick, L. A. , 2010, “ Characterization of Commercial Rigid Polyurethane Foams Used as Bone Analogs for Implant Testing,” J. Mater. Sci. Mater. Med., 21(5), pp. 1453–1461. [CrossRef] [PubMed]
Thompson, J. D. , Benjamin, J. B. , and Szivek, J. A. , 1997, “ Pullout Strengths of Cannulated and Noncannulated Cancellous Bone Screws,” Clin. Orthop. Relat. Res., 341, pp. 241–249. [CrossRef] [PubMed]
ASTM, 2012, “ Standard Specification for Rigid Polyurethane Foam for Use as a Standard Material for Testing Orthopaedic Devices and Instruments,” ASTM International, West Conshohocken, PA, Standard No. ASTM F1839-08(2012).
Linde, F. , Hvid, I. , and Pongsoipetch, B. , 1989, “ Energy Absorptive Properties of Human Trabecular Bone Specimens During Axial Compression,” J. Orthop. Res., 7(3), pp. 432–439. [CrossRef] [PubMed]
Linde, F. , and Hvid, I. , 1989, “ The Effect of Constraint on the Mechanical Behaviour of Trabecular Bone Specimens,” J. Biomech., 22(5), pp. 485–490. [CrossRef] [PubMed]
Lotz, J. C. , Gerhart, T. N. , and Hayes, W. C. , 1990, “ Mechanical Properties of Trabecular Bone From the Proximal Femur: A Quantitative CT Study,” J. Comput. Assist. Tomogr., 14(1), pp. 107–114. [CrossRef] [PubMed]
Mosekilde, L. , Mosekilde, L. , and Danielsen, C. , 1987, “ Biomechanical Competence of Vertebral Trabecular Bone in Relation to Ash Density and Age in Normal Individuals,” Bone, 8(2), pp. 79–85. [CrossRef] [PubMed]
Kopperdahl, D. L. , and Keaveny, T. M. , 1998, “ Yield Strain Behavior of Trabecular Bone,” J. Biomech., 31(7), pp. 601–608. [CrossRef] [PubMed]
Patel, P. S. , Shepherd, D. E. , and Hukins, D. W. , 2010, “ The Effect of Screw Insertion Angle and Thread Type on the Pullout Strength of Bone Screws in Normal and Osteoporotic Cancellous Bone Models,” Med. Eng. Phys., 32(8), pp. 822–828. [CrossRef] [PubMed]
Krenn, M. H. , Piotrowski, W. P. , Penzkofer, R. , and Augat, P. , 2008, “ Influence of Thread Design on Pedicle Screw Fixation,” J. Neurosurg. Spine, 9(1), pp. 90–95. [CrossRef] [PubMed]
Chapman, J. , Harrington, R. , Lee, K. , Anderson, P. , Tencer, A. , and Kowalski, D. , 1996, “ Factors Affecting the Pullout Strength of Cancellous Bone Screws,” ASME J. Biomech. Eng., 118(3), pp. 391–398. [CrossRef]
Caglar, Y. S. , Torun, F. , Pait, T. G. , Hogue, W. , Bozkurt, M. , and Özgen, S. , 2005, “ Biomechanical Comparison of Inside–Outside Screws, Cables, and Regular Screws, Using a Sawbone Model,” Neurosurg. Rev., 28(1), pp. 53–58. [PubMed]
Poukalova, M. , Yakacki, C. M. , Guldberg, R. E. , Lin, A. , Gillogly, S. D. , and Gall, K. , 2010, “ Pullout Strength of Suture Anchors: Effect of Mechanical Properties of Trabecular Bone,” J. Biomech., 43(6), pp. 1138–1145. [CrossRef] [PubMed]
Yakacki, C. M. , Poukalova, M. , Guldberg, R. E. , Lin, A. , Gillogly, S. , and Gall, K. , 2010, “ The Effect of the Trabecular Microstructure on the Pullout Strength of Suture Anchors,” J. Biomech., 43(10), pp. 1953–1959. [CrossRef] [PubMed]
Mosekilde, L. , and Mosekilde, L. , 1986, “ Normal Vertebral Body Size and Compressive Strength: Relations to Age and to Vertebral and Iliac Trabecular Bone Compressive Strength,” Bone, 7(3), pp. 207–212. [CrossRef] [PubMed]
Cook, S. D. , Salkeld, S. L. , Stanley, T. , Faciane, A. , and Miller, S. D. , 2004, “ Biomechanical Study of Pedicle Screw Fixation in Severely Osteoporotic Bone,” Spine J., 4(4), pp. 402–408. [CrossRef] [PubMed]
Inceoglu, S. , Ferrara, L. , and McLain, R. F. , 2004, “ Pedicle Screw Fixation Strength: Pullout Versus Insertional Torque,” Spine J., 4(5), pp. 513–518. [CrossRef] [PubMed]
Ryken, T. C. , Clausen, J. D. , Traynelis, V. C. , and Goel, V. K. , 1995, “ Biomechanical Analysis of Bone Mineral Density, Insertion Technique, Screw Torque, and Holding Strength of Anterior Cervical Plate Screws,” J. Neurosurg., 83(2), pp. 324–329. [CrossRef]
Chen, L.-H. , Tai, C.-L. , Lai, P.-L. , Lee, D.-M. , Tsai, T.-T. , Fu, T.-S. , Niu, C.-C. , and Chen, W.-J. , 2009, “ Pullout Strength for Cannulated Pedicle Screws With Bone Cement Augmentation in Severely Osteoporotic Bone: Influences of Radial Hole and Pilot Hole Tapping,” Clin. Biomech., 24(8), pp. 613–618. [CrossRef]
Edwards, W. T. , Zheng, Y. , Ferrara, L. A. , and Yuan, H. A. , 2001, “ Structural Features and Thickness of the Vertebral Cortex in the Thoracolumbar Spine,” Spine, 26(2), pp. 218–225. [CrossRef] [PubMed]
Hildebrand, T. , and Ruegsegger, P. , 1997, “ A New Method for the Model-Independent Assessment of Thickness in Three-Dimensional Images,” J. Microsc. Oxford, 185(1), pp. 67–75. [CrossRef]
Hildebrand, T. , Laib, A. , Muller, R. , Dequeker, J. , and Ruegsegger, P. , 1999, “ Direct Three-Dimensional Morphometric Analysis of Human Cancellous Bone: Microstructural Data From Spine, Femur, Iliac Crest, and Calcaneus,” J. Bone Miner. Res., 14(7), pp. 1167–1174. [CrossRef] [PubMed]
Nagaraja, S. , Awada, H. K. , Dreher, M. L. , Gupta, S. , and Miller, S. W. , 2013, “ Vertebroplasty Increases Compression of Adjacent IVDs and Vertebrae in Osteoporotic Spines,” Spine J., 13(12), pp. 1872–1880. [CrossRef] [PubMed]
Battula, S. , Schoenfeld, A. J. , Sahai, V. , Vrabec, G. A. , Tank, J. , and Njus, G. O. , 2008, “ The Effect of Pilot Hole Size on the Insertion Torque and Pullout Strength of Self-Tapping Cortical Bone Screws in Osteoporotic Bone,” J. Trauma Acute Care Surg., 64(4), pp. 990–995. [CrossRef]
Nagaraja, S. , Palepu, V. , Peck, J. H. , and Helgeson, M. D. , 2015, “ Impact of Screw Location and Endplate Preparation on Pullout Strength for Anterior Plates and Integrated Fixation Cages,” Spine J., 15(11), pp. 2425–2432. [CrossRef] [PubMed]

Figures

Grahic Jump Location
Fig. 1

Representative micro-CT images of different densities of closed cell foams (CCF), open cell foams (OCF), and human vertebral trabecular bone

Grahic Jump Location
Fig. 2

Screw pullout testing setup of closed cell foam (left), open cell foam (center), and cadaveric vertabra (right)

Grahic Jump Location
Fig. 3

(a) Volume fraction (mm3/mm3) of different grades of open cell foams, closed cell foams, and cadaveric trabecular bone. F symbol indicates that foam grade is similar (p ≥ 0.50) to female cadaveric specimens. M symbol indicates foam grade is similar (p ≥ 0.36) to male cadaver specimens, (b) strut thickness (mm) of different grades of foam and cadaveric specimens. All grades of foam were significantly different from each other (p < 0.002).

Grahic Jump Location
Fig. 4

(a) Strut spacing (mm) of different grades of foam and cadaveric specimens and (b) material density (mg HA/cc) of different grades of foam and cadaveric specimens. All grades of foam had significantly different density and strut spacing compared to each other (p < 0.001).

Grahic Jump Location
Fig. 5

(a) Peak pullout force (PPF) for cadaveric specimens and different grades of foam (b) pullout stiffness for cadaveric specimens and different grades of foam (c) work to PPF for cadaveric specimens and different grades of foam and (d) work after PPF for cadaveric specimens and different grades of foam. F symbol indicates that foam grade was similar (p ≥ 0.66) to female cadaveric specimens. M symbol indicates that foam grade was similar (p ≥ 0.15) to male cadaveric specimens.

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In